1. Field of the Invention
The present invention relates to a multichip light emitting diode (LED) package, and more particularly to a multichip light emitting diode package with a substrate having a non-plane surface including a plurality of sectioned-surfaces for disposing LEDs.
2. Description of the Prior Art
As a good light source and device made by semiconductor material, LEDs possess advantages of small size, long life-time, low driving voltage, rapid response, and good oscillation-proof, etc.
By changing the semiconductor materials and device structures, LEDs with different visible and invisible colors can be designed, wherein AlGaAs, InGaAlP and InGaN are suitable for producing LEDs with high luminance over 1000 mcd.
When producing red or infrared LEDs with high luminance by AlGaAs, an LPE process and DE structure devices are used for industrial mass production.
InGaAlP can be used to produce red, orange, yellow and yellow-green LEDs, and an MOVPE (Metal Organic Vapor Physical Epitaxy) process, double hetero (DH) junction structures, and quantum well (QW) structures are provided in efficient mass production. FIG. 1 shows a schematic cross-sectioned view of a traditional InGaAlP/GaAs or InGaAlP/GaP yellow LED chip 10. An InGaAlP epitaxial layer 14 is formed on an N-type GaAs substrate 13. A positive bond pad 11 is formed by gold (Au) for being connected to an anode package leg, and a negative bond pad 12 is formed by Al or Au and connected to a cathode package leg.
InGaN is suitable for producing green, blue and ultraviolet LEDs with high luminance by high temperature MOVPE processes, wherein DH structures and QW structures are used, too. FIG. 2 shows a schematic cross-sectioned view of a traditional blue LED chip 20. A substrate 23 is formed by transparent sapphire. An upper P-type InGaN epitaxial layer 25 and a lower N-type InGaN epitaxial layer 24 are deposited on the substrate 23. A positive bond pad 21 is formed on the P-type InGaN epitaxial layer 25 for being connected to an anode package leg, and a negative bond pad 22 is formed on the N-type InGaN epitaxial layer 24 for being connected to a cathode package leg. Alternatively, the N-type InGaN epitaxial layer 24 can be epitaxied on the P-type InGaN epitaxial layer 25. As shown in FIG. 2, the sapphire substrate 23 as a support base results in a different connecting type for the negative bond pad 22 from FIG. 2.
Color light other than red, green and blue light can be obtained by adjusting the intensities of the primary colors of red, green and blue lights. If there are red, blue, and green primary colors, by adjusting the intensity of each color, a full color light source can be obtained. FIG. 3 shows a schematic cross-sectioned view of a conventional full color LED chip, a red, a green and a blue primary color LEDs are packaged with chips 301, 302 and 303 in a row or in array by die bond on a printed circuit board 305. The power of the red LED is applied to the positive pad 306 and via the ground pad 304 on the printed circuit board 305 to the negative of the source, the same method is applied to the green and blue LEDs. Generally, a constant current source 20 mA is used as the power source. For example, 20 mA with voltage of 2V is applied to the red LED 301; 20 mA with voltage of 3.5 V is applied to the green LED 302 and 20 mA with voltage of 3.5 V is applied to the blue LED 303, a white light is obtained and the power consumption is 180 mW (20×2+20×3.5+20×3.5=180 mW); if full color is needed, the current is still kept at 20 mA, but by control the lighting period of each LED to combined the light, different color lights can be obtained if desired.
For increasing light brightness, a multichip light emitting diode package encapsulating multiple LED chips is developed. And, as the rapid development of mobile phones and PDAs (Personal Digital Assistants), there is a request to develop colorful LED panels to display colorful images. Therefore, it is necessary to develop a multichip LED package with three light emitting diodes (generally red, blue and green).
FIG. 4 is a schematic cross-sectioned view of a conventional multichip light emitting diode package, two LED chips 41 and 42 are disposed on a flat surface of a printed circuit board 40, and a dome-shaped epoxy resin 43 is coated on the printed circuit board 40 for encapsulating the two LED chips 41 and 42. The light emitting from the two LED chips 41 and 42 travels through the epoxy resin 43 and enters the air. Since the light of the two LED chips 41 and 42 travels through two media with different indices of refraction, the light emitting from the two LED chips 41 and 42 is deflected at the boundary between the epoxy resin 43 and the air according to the snell's law of n1 sin θ1=n2 sin θ2. As a result, beam divergence happens, as shown in FIG. 4. Therefore, when the two LED chips 41 and 42 emit same color light, the multichip light emitting diode package would emit light with non-uniform brightness. When the two LED chips 41 and 42 emit different color light, the multichip light emitting diode package would emit light with non-uniform hues.
FIG. 5 is a schematic cross-sectioned view of a conventional white light multichip light emitting diode package, a red LED chip 51, a green LED chip 52 and a blue LED chip 53 are disposed on a flat surface of a printed circuit board 50. A molding epoxy resin 54 is coated on the printed circuit board 50 to encapsulate the three LED chips 51, 52 and 53. The light emitting from each of the red LED chip 51, green LED chip 52 and blue LED chip 53 travels through two media with different indices of refraction. The light of the red LED chip 51, green LED chip 52 and blue LED chip 53 is deflected at boundary between the epoxy resin 54 and the air according to the snell's law. Beam divergence happens. As a result, the red, green and blue lights of the three LED chips 51, 52 and 53 cannot be uniformly mixed after traveling out the epoxy resin 54. The white light multichip light emitting diode package cannot provide uniform white light.
The conventional multichip light emitting diode package structure as above cannot provide illuminating light with uniform brightness and hues. The illumination quality of them is adversely influenced. Therefore, an improved multichip light emitting diode package structure is developed, which is as shown in FIG. 6. Two LED chips 61 and 62 are disposed on a flat surface of a printed circuit board 60. A double dome-shaped epoxy mold 63 is coated on the printed circuit board 60 for encapsulating the two LED chips 61 and 62, each of the double dome-shaped epoxy mold 63 is formed above one of the two LED chips 61 and 62. However, it is difficult to form the double dome-shaped epoxy mold 63 by mold injection. And, it is not easy to control the illumination of the two LED chips 61 and 62 to attain consistence.
Accordingly, it is an intention to provide an improved multichip light emitting diode package structure, which can overcome the above drawbacks.